Propellant composition

ABSTRACT

A solid composite propellant composition consisting essentially of a conventional binder containing modified ammonium perchlorate which consists of whisker-like single crystals without inclusions and ranging in diameter from about 1 to 40 microns.

United States Patent McBride et al.

1451 Nov. 11, 1975 PROPELLANT COMPOSITION 3.203.842 8/1965 066116149.131 1.301.712 1/1967 Mnhuup! e! 211 149,-1 [75] [memory Y' McBr'dei3.359.3511 12/1967 06am; 264/3 R Flnflegani Adicofi, Of 3.383.180 4/1968Krulik e! 111. 149/76 x m Lake. lf- 3.454.437 7/1969 Yumazaki et 61149121 1731 AS99139 The Wed S919 America 85 3123213 1/133?35323511.?ijiiijjjiii'"Jji'ij 113132;? "eprmmed P 3.673.013 6/1972 Lane61211 14911 1.1 x Navy, Washington. DC.

[22] Filed: Nov. 24, 1970 Primary E.\r1mi:1er\ 'erlin R. PendegrassAssistant Examiner-P. A. Nelson 7 1 [*1] App! 97'467 Attorney, Agent. orFirm-R S. Sciascia; R0 Miller;

Lloyd E. K. Pohl [52] US. Cl. 149/195; 149/2; 149/199; 149/76; 149/113[51] Int. Cl. C06P 45/10 [57] ABSTRACT [58] Fi f Search 149 p 17 113 217 A solid composlte pronellant comp0sm0n cons1stmg 149 19 19 4essential] of a conventional b1nder containing modi- 5, 9. 26 /3 R 1 Ified ammonium perchlorate which cons1sts of whisker- [56] R fe cu d likesingle crystals without inclusions and ranging in UNITED STATES PATENTSdiameter from about 1 to 40 microns.

2.991.168 7/1961 19.11161 149/2 4 Claims, 1 Drawing Figure O z 1.0 O a0.8 U] E 0 0.6 E

Z 0.4 ,i 1 [I PRESSURE 1N 1 s1A US. Patent Nov. 11,1975 3,919,012

RATE IN INCH/SECOND 0 O b (D O r n u l r 1 1 'I O0 ZOO 400 600 1 OOOZOOO 4000 PRESSURE IN PSIA INVENTORS.

WILLIAM R. MCBRIDE WILLIAM G. F'QNNEGAN ARNOLD ADICOFF BY ROY MILLERATTORNEY.

PROPELLANT COMPOSITION STATEMENT OF GOVERNMENT INTEREST The inventiondescribed herein may be manufactured and used by or for the Governmentof the United States of America for governmental purposes without thepayment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION The invention relates to improved solidpropellants, and more particularly to a composite propellant formulationcontaining modified ammonium perchlorate crystals.

As a result of the need in modern rocket technology greater refinementin the development of solid propellants has become necessary. Morepowerful rocket ingredients are constantly being sought to provideimproved environmental resistant qualities, improved physicalproperties, better and unique burning rate characteristics, and to yieldimproved thrust-time characteristics. The present invention utilizes amodified form of ammonium perchlorate crystals which provides improvedphysical and chemical properties over compositions using regular grindammonium perchlorate crystals.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a graph whichsummarizes and compares the burning rates for the propellant strands ofpropellant formulations containing commercially ground ammoniumperchlorate, nominal 40-;1. whisker ammonium perchlorate and nominal 3-whisker ammonium perchlorate.

BRIEF DESCRIPTION OF THE INVENTION Broadly speaking, the presentinvention resides in a composite propellant composition comprising aconventional propellant binder and modified ammonium perchlorate cystalsin the form of whiskers having a length to diameter ratio of about 5:1to about 100:]. Other conventional constituents have been incorporated,such as ballistic modifiers.

The conventional composite propellant binders include functionalpolybutadienes such as hydroxy or carboxyterminated polybutadienepolymers, butadiene acrylic acid copolymers, butadiene acrylic acidacrylonitrile terpolymer, polyesters, polysulfides, polyurethanes,plastisols, etc. Other conventional constituents include metals such asaluminum and magnesium, metal organic compounds, metallic hydrides, andvarious ballistic modifiers, such as iron oxide, potassium perchlorate,and potassium dichromate.

Ammonium perchlorate whiskers used in the examples herein were nominal40- diameter and nominal 3-p. diameter size. The larger diameterwhiskers were prepared by feeding ammonium perchlorate solution belowsaturation through commercially available porous glass tubes. Thenominal 3-p. diameter whiskers were formed by the process described incopending patent application Ser. No. 79,680 filed Oct. 9, 1970, whichcomprises feeding ammonium perchlorate solution through porous glasstubing which is carefully and thinly coated on the outside with siliconeadhesive. Whiskers of varying size prepared by other means may be used.

The following examples illustrate the present invention:

EXAMPLE I Ingredients by weight Carboxyterminated polybutadieneprepolymers 24 (CTPB) Ammonium perchlorate (nominal 40p) 76 The ammoniumperchlorate crystals used herein are characterized as being whisker-likeorthorhombic single crystals without inclusions and having a length todiameter ratio of from about 5:] to about lOO1l. They were blended intothe carboxyterrninated polybutadiene prepolymer in a conventional mixerto form a homogenous mixture which was cast and cured into predeterminedshapes and tested. Samples of this formulation were also cast intoburning rate strands, sections of which were cut parallel andperpendicular to the direction of extrusion to determine the whiskeroxidizer orientation. At right angles to the direction of extrusion manyof the crystals showed triangular cross-section, and a cut parallel tothe direction of extrusion showed a columnar structure of the whiskersin the propellant.

EXAMPLE ll by weight Ingredients Carboxyterminated polybutadieneprepolymer Ammonium perchlorate (nominal 3p) Aluminum (nominal IS Theabove ingredients were processed as in Example I, and the mixture castinto preforms, cured and tested. A sample was thinned after mixing andprior to cure and dispersed sufficiently for optical examination underthe microscope. It was noted that although the whiskers were brokenduring mixing, a length to diameter ratio ranging from 5:1 and l0:l wasmaintained.

EXAMPLE Ill Ingredients by weight Carboxyterminated polybutadieneprepolymer 24 Ammonium perchlorate (nominal 3p.) 76

EXAMPLE IV Ingredients 1: by Weight Carboxyterrninated polybutadieneprepolymer I 24 Ammonium perchlorate (15p. grind) 76 The ingredientswere blended together in a conventional mixer and the homogeneous pasteresulting therefrom was cast into burning rate strands. The strands wereburned in the manner described hereinabove and burning times andtemperatures were re- 3 corded and the burning rates were calculated andplotted.

1n the single FIGURE in the form of a graph there is shown comparativeburning rates for propellant strands comprising the formulation (ExampleIV) containing commercial grind ammonium perchlorate designated curve A;the formulation (Example 1) containing nominal 40-;1. whisker ammoniumperchlorate, designated curve B; and formulation (Example [11)containing nominal 3-11. whisker ammonium perchlorate, designated curveC. A sigmoid curve for the ground ammonium perchlorate formulation(Example 1V) is observed. All data acquired with the whiskerformulations conform to the simple expression r aP (absence of sigmoidshape) where r is the burning rate, a is a constant, P is the pressureand n is the pressure exponent. The pressure exponents for curves B andC are 0.584 and 0.567, respectively. The difference in burning rates forcurves B and C is attributed to the difference in effective particlesize of the whisker ammonium perchlorate of the two formulations.

The comparison illustrates that the whisker ammonium perchlorateincorporated into a propellant fonnulation provides burning rates whichconform to the sim plified linear rate equation and its resultant linearregression as plotted and shown in the single FIGURE. (Ground ammoniumperchlorate gives a sigmoid buming rate pressure curve). The pressureexponent for the log rate vs. log pressure plot is constant,approximately 0.58. The burning rate of the propellant is apparentlycontrolled by the diameter of the whiskers in that the rate increaseswith a decrease from 401.; to 3-1.. nominal whisker diameter. Althoughmixing the propellant formulation reduces the length-to-diameter ratioof the whiskers, the material is still capable of being oriented with anextrusion process.

Catalyzed ammonium perchlorate whiskers prepared by the processdescribed in copending patent application Ser. No. 79,680 filed Oct. 9,1970 referenced hereinbefore were also incorporated into conventionalcomposite propellant binders. Predetermined amounts of catalyticmaterials incorporated into the ammonium perchlorate whiskers includedsuch burning rate modifiers as potassium perchlorate, ammoniumpermanagnate, ammonium dichromate and iron oxide. Any burning ratemodifier having ions which can be incorporated into the ammoniumperchlorate crystals can be used. Several batches of propellantformulation comprising about 25 percent by weight carboxyterminatedpolybutadiene prepolymer and about percent catalyzed ammoniumperchlorate whiskers were prepared, cast and cured. Some was extrudedinto burning rate strands and routinely tested. They showed unusualcombustion properties such as higher burning rate exponent, weredifficult to ignite and sustain burning at low pressure.

Both the ammonium perchlorate whiskers and the catalyzed ammoniumperchlorate whiskers of micron and submicron diameter can be used inconjunction with a large variety of binders and fuels to produce animproved solid composite propellant grain.

What is claimed is:

l. A solid propellant formulation comprised of an oxidizer phaseconsisting of whisker-like crystals of ammonium perchlorate incombination with at least one solid propellant binder selected from thegroup consisting of hydroxy terminated polybutadiene, carboxy terminatedpolybutadiene butadiene acrylic acid copolymers, butadiene acrylic acidacrylonitrile terpolymer, polyesters, containing constituents selectedfrom the group consisting of metals, metal organic compounds, metallichyclrides, ballistic modifiers and combinations thereof.

2. The formulation in accordance with claim 1 wherein said whisker-likecrystals are of varying dimensions ranging in a length to diameter ratioof from about 5:1 to about :1.

3. The formulation in accordance with claim 1 wherein said oxidizerphase consists of catalyzed ammonium perchlorate whiskers which consistessentially of ammonium perchlorate and a predetermined amount of aburning rate modifier.

4. The formulation in accordance with claim 3 wherein said burning ratemodifier is a member selected from the group consisting of potassiumperchlorate, ammonium permanganate, ammonium dichromate and iron oxide.

1. A SOLID PROPELLANT FORMULATION COMPRISED OF AN OXIDIZER PHASECONSISTING OF WHISKERS-LIKE CRYSTAL OF AMMONIUM PERCHLORATE INCOMBUSTION WITH AT LEAST ONE SOLID PROPELLANT BINDER SELECTED FROM THEGROUP CONSISTING OF HYDROXY TERMINATED POLYBUTADINE, CARBOXY TERMINATEDPOLYBUTADINE BUTADIENE ACRYLIC ACID COPOLYMERS, BUTADIENE ACRYLIC ACIDACRYLONITRITE TEPOLYMER, POLYESTERS, CONTAINING CONSTITUENTS SELECTEDFROM THE GROUP CONSISTING OF METALS, METAL ORGANIC COMPOUNDS, METALLICHYCLRIDES, BALLISTIC MODIFERS AND COMBINATIONS THEREOF.
 2. Theformulation in accordance with claim 1 wherein said whisker-likecrystals are of varying dimensions ranging in a length to diameter ratioof from about 5:1 to about 100:1.
 3. The formulation in accordance withclaim 1 wherein said oxidizer phase consists of catalyzed ammoniumperchlorate whiskers which consist essentially of ammonium perchlorateand a predetermined amount of a burning rate modifier.
 4. Theformulation in accordance with claim 3 wherein said burning ratemodifier is a member selected from the group consisting of potassiumperchlorate, ammonium permanganate, ammonium dichromate and iron oxide.